1. Technical Field
The present invention relates to a physical quantity sensor and an electronic apparatus.
2. Related Art
In recent years, techniques for realizing a small and high-sensitivity physical quantity sensor using a silicon MEMS (Micro Electro Mechanical System) technique, for example, have been developed.
For example, JP-T-2009-537803 discloses a physical quantity sensor (acceleration sensor) with a mass body having two wings that can rotate around a torsion web. In the physical quantity sensor disclosed in JP-T-2009-537803, a through hole is provided in each of the two wings so that torsion of the same magnitude and opposite directions with respect to the torsion web causes a damping torque of the same magnitude. In addition, the physical quantity sensor has a first electrode below one wing and a second electrode below the other wing, and detects acceleration on the basis of the capacitance between one wing and the first electrode and the capacitance between the other wing and the second electrode.
In addition, for example, JP-A-2007-298405 discloses a physical quantity sensor in which a movable electrode, which is movably supported by a fixed section of a semiconductor layer with a beam section interposed therebetween so as to have asymmetric mass balance and which moves according to the displacement of the physical quantity in a thickness direction of the semiconductor layer, and a fixed electrode, which is formed on a support substrate, are disposed so as to face each other with a gap therebetween. The physical quantity sensor disclosed in JP-A-2007-298405 detects a physical quantity on the basis of the capacitance detected according to the size of the gap between the movable electrode and the fixed electrode.
However, an attempt to reduce the size of the physical quantity sensors disclosed in JP-T-2009-537803 and JP-A-2007-298405 causes a reduction in the electrode area to form the capacitance. For this reason, in order to improve the detection sensitivity without changing the resonant angular frequency, it is necessary to reduce a gap between electrodes (distance between a movable electrode section and a fixed electrode section). However, even if the desired detection sensitivity is obtained by reducing the gap between electrodes, capacitance between the electrodes in a state where acceleration is not applied, that is, initial capacitance tends to increase. An increase in the initial capacitance may become a noise gain to cause a deterioration of the noise characteristic.